High molecular weight non crystalline poly (alpha-olefin) have wide spread applications in many fields. For example poly (1-hexene) acts as viscosity index improver in lubricating oils whereas poly (1-octene) is used as drag reducing additive to reduce friction loss or drag for pumpable fluid through pipelines.
Ziegler Natta catalysts are used for polymerization of olefins at moderate temperature and pressure. The catalyst generally comprises of a transition metal halide such as titanium trihalide or tetrahalide and an organoaluminum compound such as alkyl aluminum or alkyl aluminum halide. The transition metal compound can be supported on an inorganic or organic support.
There are many heterogeneous catalysts cited in prior art which polymerize alpha-olefin containing four or more carbon atoms. For example U.S. Pat. No. 4,613,712 discloses a catalyst composition prepared by treatment of silica with ethyl magnesium chloride in tetrahyrofuran and treatment with excess titanium tetrachloride. This catalyst was used for the polymerization of 1-hexene, 1-octene, and 1-decene at 70.degree. C. using triethyl aluminum as cocatalyst. European Patent 281,924 discloses a catalyst composition prepared by treatment of magnesium chloride ethanol adduct with titanium alkoxide in decane at 80.degree. C. followed by addition of diethyl aluminum chloride. The catalyst was used for polymerizing 1-butene, 1-hexene, and 1-octene in n-heptane as diluent at 50.degree. C. U.S. Pat. No. 528,117 describes a catalyst using transition metal alcholate, magnesium chloride and an aliphatic ester in hydrocarbon medium. The catalyst was used for polymerization of ethylene and copolymerization with alpha-olefins.
However these catalysts described in prior art does not provide super high molecular weight poly(alpha-olefin) suitable as drag reducer in pipelines. U.S. Pat. No. 4,415,714 discloses a catalyst, namely, TiCl.sub.3, 1/3AlCl.sub.3 along with diethyl aluminum chloride for the preparation of super high molecular weight polyolefin suitable as drag reducer. Furthermore, U.S. Pat. No. 4,493,904 describes polymerization of 1-octene using TiCl.sub.3.1/3AlCl.sub.3 along with diethyl aluminum chloride as cocatalyst and diethylether as electron donor. Similarly U.S. Pat. No. 4,433,123 and U.S. Pat. No. 4,358,572 describes preparation of super high molecular weight poly (1-octene) suitable as drag reducer using same catalyst/cocatalyst combination. U.S. Pat. No. 4,384,089 describes copolymerization of 1-decene and 1-butene using TiCl.sub.3.1/3AlCl.sub.3 /diethyl aluminum chloride catalyst system.
However, catalysts based on TiCl.sub.3.1/3AlCl.sub.3 /Diethyl aluminum chloride suffer from many drawbacks as follows:
1. These catalysts leave high chloride residue in the product which is undesirable in further applications.
2. This requires expensive processing steps for neutralization of chloride.
3. also use of diethylaluminum chloride containing catalyst, cause evolution of HCI during the catalyst destruction step.
4. Furthermore handling of TiCl.sub.3.1/3AlCl.sub.3, is rendered difficult in view of its extreme sensitivity of oxygen and corresponding deactivation.